In a communication area where the reception power of a signal transmitted from a base station becomes weak and a terminal not capable of ensuring sufficient reception power exists, a relay station is used that amplifies the reception power of a signal transmitted from the base station and relay-transmits the signal to a terminal. In the relay station, the power of a signal received from the base station is amplified and the signal after the power amplification is retransmitted to a terminal.
Here, in a full-duplex type relay station performing transmission and reception at a same time and with a same frequency, a phenomenon called a “wraparound” occurs where the transmission signal of the self-station turns out to be received by the self-station. There is a possibility that, owing to the repetition of the wraparound, the power of a signal input to an amplifier included in the relay station exceeds an assumption at the time of the designing of the relay station and the amplifier oscillates. In addition, when the wraparound is repeated, a processing delay or a propagation delay within the relay station is accumulated. Therefore, an interference between symbols (hereinafter, simply referred to as an “intersymbol interference” in some cases) at the time of the reception of a signal in the terminal occurs, and reception quality is deteriorated.
As a technique of the related art for minimizing the deterioration of reception quality due to the wraparound, there is a technique for controlling, on the basis of a path loss between a relay station and a terminal or a path loss between a base station and the relay station, the transmission power of the relay station so that reception quality in the terminal is maximized. For example, there is a technique of the related art for obtaining the transmission power of a relay station, which maximizes reception quality in a terminal, in a case where a processing delay in the relay station is equal to one symbol length of a desired signal and no propagation delay exists.
A technique of the related art is disclosed in Riihonen, T. et. al., “Optimized gain control for single-frequency relaying with loop interference,” Wireless Communications, IEEE Transactions on, Vol. 8, No. 6, pp. 2801-2806, 2009.